1. Field of the Invention
The present invention relates generally to a tester including a driver, a comparator and a switching or change-over circuit for testing integrated circuits or devices (ICs). More particularly, the present invention is concerned with a change-over circuit incorporated in an IC tester apparatus for allowing load circuits to be automatically connected to a device under test in a driver-inhibited (disabled) mode and which circuit is implemented by employing diode-bridge type analog switches.
2. Description of the Prior Art
Before entering into description of the invention, a configuration of a prior art circuit for changing over loads for a device to be tested (hereinafter also referred to as the device under test) will briefly be elucidated by reference to FIG. 3 of the accompanying drawings.
In FIG. 3, a reference numeral 21 denotes a driver circuit, 22 denotes a device under test, 23 denotes a current load circuit, 24 denotes a capacitive load circuit, 25 denotes a comparator, and reference numerals 26 to 29 denote switches, respectively.
In operation, a drive signal is applied to a terminal 31 while an ON/OFF control signal is applied to a terminal 35. Further, a negative voltage V.sub.T is applied to a terminal 33, and a constant current is supplied through terminals 32 and 34 as a load current. With the circuit structure shown in FIG. 3, the current load circuit 22, the capacitive load circuit 24 and the comparator 25 can be changed over to operative state only when the output of the driver circuit 21 is disabled or inhibited by the switch 26.
When the switch 26 is turned on, the switches 27 to 29 are turned off, while the latter are turned on upon turning-off of the switch 26, as a result of which the current load circuit 23 and the capacitive load circuit 24 are switched on a real-time basis. On the other hand, when the driver is enabled (i.e. when the driver is released from the inhibited state), the current load circuit 23 and the capacitive load circuit 24 are disconnected.
As will be appreciated from the above description, in the case of the prior art circuit shown in FIG. 3, there are required three switches for changing over the current load circuit 23 and the capacitive load circuit 24, i.e. the switches 27 and 28 in association with the current load circuit 23 and the switch 29 in association with the capacitive load circuit 24, respectively, which in turn means that the circuits for operating these switches 27 to 29 are additionally required, thus giving rise to problems in respect to the current consumption as well as the manufacturing cost.